2004 f150 steering

I have a 2004 f150 Lariat super crew, the power steering gets hard to turn when starting off, or braking into a turn. last summer it did this and the hubs where bad,after i replaced them it went away, now 7 months later its back. it has the 5.4 liter..any ideas?

Now, this Monday when i left for work in the morning the problem is gone, the steering is fine now. What could it be?